(a) Field of the Invention
The present invention relates to a positive active material for a lithium secondary battery and a preparation method of the same, and more particularly, to a positive active material for a lithium secondary battery and a lithium secondary battery having improved storage characteristics and cycle-life characteristics at a high temperature, and improved safety characteristics, and a method of preparing the same.
(b) Description of the Related Art
A lithium secondary battery is required to have good cycle-life characteristics, safety characteristics, and storage characteristics at a high temperature. An important factor in cycle-life characteristics of a battery is the characteristics of positive and negative active materials. Recently, colossal improvements have been made in the field of negative active material, but there are still a lot of problems in the field of positive active material. Research on positive active material is particularly required, because safety and storage characteristics of a battery at a high temperature are dependant on the characteristics of the positive active material.
Representative positive active materials of a lithium secondary battery include LiCoO2, LiNiO2 and LiMn2O4. Among them, LiNiO2 has the largest capacity but it cannot be easily utilized because of safety problem, LiMn2O4 has the smallest specific capacity and is thus not suitable for a positive active material, and LiCoO2 has poor storage characteristics at a high temperature.
A lot of research is underway to overcome the above-mentioned problems. There are three representative research approaches. One of them is improving storage characteristics at a high temperature by coating LiMn2O4 with metal carbonate; another is improving cycle-life and safety characteristics by coating LiCoO2 with metal oxide; the third is improving the safety of the battery by enhancing structural and thermal characteristics by the use of various dopants.
Although the above-mentioned methods improve cycle-life characteristics at room temperature, they don't improve storage characteristics and cycle-life characteristics at a high temperature.